Galactic Rim

The Galactic Rim (or The Rim) is the region near the edge of the Milky Way galaxy and the outer reaches of space explored by the younger races. The older races, or First Ones, have traveled beyond the Rim into the void between galaxies.

"The Rim" is also used as a generic term that refers to the outermost extent of known space within the galaxy itself; as new systems are being charted and explored all the time, the idea of the Rim is an ever-changing concept.[1]

Before its destruction, the planet Z'ha'dum was located near the Rim[2].